1. Field of the Invention
The present invention relates to an optical element.
2. Description of the Related Art
There has been proposed an optical element 10 that adjusts the amount of transmitting light using an electrowetting phenomenon (see JP-A-2000-356792).
The optical element 10 includes, as shown in FIG. 14, a sealed container 18 having first and second end walls 12 and 14 that face each other in the thickness direction, and a sidewall 16 that connects the end walls 12 and 14; a first polar or conductive liquid 20 that is encapsulated in the container 18; and a second liquid 22 that is encapsulated in the container 18 and has a transmittance higher than that of the first liquid 20.
A first electrode 24 is formed on the entire inner surface of the first end wall 12 that faces the inside of the container 18, and a hydrophilic film 30 is formed such that it covers the first electrode 24.
A second electrode 26 is formed on the entire inner surface of the second end wall 14 that faces the inside of the container 18, and an insulating film 28 is formed such that it covers the second electrode 26.
A water repellent film 32 is formed in a circular region that is part of the insulating film 28 and centered on the center of the second end wall 14. A hydrophilic film 34 is formed in an annular region that is part of the insulating film 28 and does not include the water repellent film 32.
Using two types of liquid as the first liquid 20 and the second liquid 22 that do not mix with each other and have a same specific gravity, only the first liquid 20 and the second liquid 22 are encapsulated in the container 18 without any other substances, such as air, contained. In this way, even when the container 18 is rotated or shook, the initial state in which only the first liquid 20 and the second liquid 22 are encapsulated in the container 18 is maintained, and the state in which a curved interface K that is convex toward the first liquid 20 is formed between the first liquid 20 and the second liquid 22 is also maintained.
When no voltage is applied across the first and second electrodes 24 and 26, the second liquid 22 is positioned on the water repellent film 32, while the first liquid 20 is positioned on the hydrophilic film 34.
When a voltage is applied to the first liquid 20 from voltage application mean to induce an electrowetting phenomenon, the interface K between the first liquid 20 and the second liquid 22 is deformed from the state indicated by the solid line to the state indicated by the broken lines shown in FIG. 14. This deformation forms a light transmission path T that passes through the first and second end walls 12 and 14 and extends in the thickness direction of the container 18.
Specifically, when no voltage is applied, the first liquid 20 entirely extends in the direction perpendicular to the light transmitting direction, as indicated by the solid line in FIG. 14, so that light transmission is blocked or reduced. On the other hand, when the application voltage is increased, the second liquid 22 comes in contact with the both end walls 12 and 14 to form the transmission path T, as indicated by the broken lines in FIG. 14. By adjusting the application voltage, the contact area between the second liquid 22 and the first end wall 12 is increased or decreased, so that the size of the transmission path T is adjusted.
To apply a voltage to the first liquid 20 from the voltage application means, the first liquid 20 always needs to be positioned over the second electrode 26 via the insulating film 28.
In the related art described above, two regions are formed on the second electrode 26, that is, the circular water repellent film 32 and the annular hydrophilic film 34, so that the first liquid 20 is positioned on the annular hydrophilic film 34 irrespective of the presence or absence of the voltage.
However, the region of the hydrophilic film 34 is an unwanted region that does not contribute to the light transmission and this unwanted region occupies a certain area, which imposes limitations on reducing the dimension of the container 18 in the direction perpendicular to the light transmitting direction, creating a disadvantage in reducing the size of the optical element 10.
Under the circumstances, it is desirable to provide an optical element that provides an advantage in reducing the size thereof and a method for manufacturing the same.